An Open Book on Closed Molding

Composites manufacturers are switching from open to closed molding and discovering the benefits and challenges of the new process.

Many tout closed molding as offering a variety of benefits—from reducing styrene emissions and cost to improving quality and increasing production volume—but open molding remains the norm within the composites industry. Brad Walter, engineering supervisor for FRP and plural component equipment, with ITW Finishing Equipment Americas, a supplier of pumping and spray equipment to the composites manufacturing industry estimated that only around 10 to 15 percent of his company’s customers have converted, and even those who have don’t use closed molding for every part.

Given its many benefits, many manufacturers are considering closed molding. But what are the exact costs and benefits of making the switch? Here, three companies across the market share their experiences, decision-making processes and opinions on open versus closed molding.

INFRASTRUCTUREOrenco Systems

Why make the switch?

Oregon-based Orenco Systems was an early adopter of closed molding. The company, which specializes in wastewater solutions, first started using the process to make fiberglass access lids in 1988. In Orenco’s case, the process was less a conversion and more a matter of adopting closed molding as the company expanded.

“We just never liked the variability and the lousy working conditions associated with open molding,” says Eric Ball, Orenco’s vice president of product development.

The company also wanted better quality parts that it could churn out at a higher volume.

“We’re not a custom molder,” Ball says. “For the most part we’re making parts for our own processes and equipment. We needed to make tens of thousands of these a year, and we needed to make nicer looking parts. Spray up just wasn’t getting us there.”

The benefits

Ball says closed molding has resulted in better quality parts for Orenco Systems. Parts made with a closed mold are more consistent and can more easily incorporate high-strength fabrics and achieve higher glass contents (regularly 40 to 50 percent and even higher, depending on what type of reinforcement glass is used) than chopped manual parts.

Orenco has also seen success in using closed molding for large tank parts, which must be watertight. According to Ball, using an open mold often resulted in pinhole leaks because of the inaccuracy of the manual lamination process. “When you do a closed molding process, you’re forcing resin through a fixed cavity, so every last air void is full of resin, and the part is the same weight every time,” Ball says. “It’s a much more exact process.”

The company has also seen quicker cycle times—less than five minutes for small, seven-pound parts that would typically take an hour or more with open molds. Large, 400-pound parts that used to take four hours in open molding are cycled in 90 minutes. Closed molding has also reduced styrene emissions from approximately 10 percent to less than 2 percent as well as improved conditions for workers. Ball says most employees don’t wear masks, and because resin isn’t being sprayed, the floor and other surfaces stay cleaner. “When you’re trying to attract high quality workers, having a nice working environment can be a huge benefit,” he says.

The challenges

While the company knew there would be a learning curve associated with closed molding, they didn’t realize how steep it would be. Mistakes were made, Ball says, and they still occur today. Early on, Orenco had to scrap a large mold they tried to make by vacuum bagging. “We tried to shoot it all at once and ended up with resin-rich areas, which then shrank, creating an inaccurate mold,” he says. “The lesson learned was that if you’re trying something new, try it on a smaller part first.” Still, he says the company was turning out good quality parts within a year of its first foray into closed mold technology.

Ball also says getting fiberglass into a closed mold is the Achilles Heel of the process. Instead of using a chopper gun, as with open molds, closed molds require rolls of fiberglass that must be cut to shape. Fiberglass in that form costs more and increases waste. As a solution, Orenco has automated the process so that robots spray fiberglass onto a preform, but that, of course, required additional investment.

Another drawback is mold cost and time to implementation. Building a sophisticated closed mold system can take months and costs many times more than an open mold for the same part. “There really is a lot to consider when determining how and when to move forward with closed molding,” Ball says. “To be successful at closed molding takes far more planning and engineering than open molding. You can’t jump into it half-heartedly. You really have to be committed to understanding the process.”

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